The invention relates to a curable composition suitable for coating ribbon matrices and glass surfaces, specifically, coating optical waveguides such as optical fibers, the coating composition having a faster cure time than was previously possible.
Optical fibers made from drawn glass have been used as a reliable transmission medium in telecommunications cables. Glass optical fibers are widely used because they have the ability to carry large amounts of information over long distances.
Optical fiber waveguides have been coated with plastic compositions of various materials in order to protect the fiber and increase its tensile strength. Optical glass fibers are generally coated with two superposed coatings. The coating which contacts the glass is a relatively soft, primary coating that must satisfactorily adhere to the fiber and be soft enough to resist microbending especially at low service temperatures. The outer, exposed coating is a much harder secondary coating that provides the desired resistance to handling forces yet must be flexible enough to enable the coated fiber to withstand repeated bending without cracking the coating.
Optical fiber coating compositions, whether they are either primary or secondary coatings, generally comprise before cure an ethylenically-unsaturated monomer or oligomer dissolved or dispersed in a liquid ethylenically-unsaturated medium and a photoinitiator, or blend of photoinitiators. The coating composition is typically applied to the optical glass fiber in liquid form and then exposed to actinic radiation to effect cure.
In practice, the most commonly used coatings have been derived from acrylates. The most widely used acrylates are those which are capable of ultraviolet radiation curing at high speed since the coatings are normally applied immediately after the glass fiber has been drawn from the molten state. Typical of such acrylates are multifunctional or (meth)acrylate terminated monomers and oligomers. The secondary coating is most often urethane-acrylate or epoxy-acrylate copolymers which also may be cured by ultra-violet radiation.
Coatings are applied to the fiber in-line during fiber drawing. As the state of fiber drawing technology has allowed for increased draw speeds to effectuate longer and thinner optical fibers, the need for coating compositions that can cure at faster rates coincident with the faster draw speeds has become more urgent. Thus, as draw speeds have increased, a need has developed for materials that cure at faster rates than available with traditional technology.
Fullerenes are hollow molecules composed only of carbon atoms which constitute an allotropic form of carbon. The skeleton structure has a steric configuration composed of a carbon ring, such as a 5-membered carbon ring or a 6-membered carbon ring. The pentagons or hexagons are required in order to allow the curvature and eventual closure of the closed surface upon itself. For further information concerning the structure of fullerenes, see, e.g., H. W. Kroto, et al., 91 CHEMICAL REVIEWS, 1213-1235 (1991).
U.S. Pat. No. 5,281,653 to Thomann, et al. describes polymer compositions produced by combining a polymer and a sufficient amount by weight of fullerenes to result in a minor change or modification in the viscoelastic properties of the fullerene-polymer compositions compared to the unmodified polymer.
U.S. Pat. No. 5,302,474 to Shackle describes solid electrochemical cells containing a solid reaction cured polymer electrolyte and a cathode composed of radiation cured polymer electrolyte and fullerene.
U.S. Pat. No. 5,530,206 to Robert, et al. discloses a coaxial cable intended to be used in the field of telecommunications comprising a semiconductor composite material comprising an undoped polymeric conductor. The undoped polymeric conductor is selected from an electronic polymeric conductor chosen from polymers and copolymers based on fullerene. The coaxial cable absorbs electromagnetic interference generated by the electronic components or connecting cables in telecommunications systems.
U.S. Pat. No. 5,759,725 to Hirao, et al. describes a photoconductor comprising a material selected from the group of fullerenes and their derivatives arranged in an amorphous structure. The fullerenes yield a photoconductor having high charge-generating efficiency by photo-irradiation.
The present inventors have found that a liquid, radiation curable composition having a fast cure time can be provided by adding fullerenes to a composition comprising a radiation curable oligomer, a free radical photoinitiator, and a reactive diluent.
There is provided a liquid, radiation curable composition for coating an optical waveguide, said composition comprising (a) a radiation curable oligomer, (b) a free radical photoinitiator, (c) a reactive diluent or mixture of reactive diluents, and (d) fullerenes.
The present coating composition for optical fibers can cure at faster rates to parallel faster draw speeds.